Okay, I can change the post to say "why was % selected as a sigil given that it was a printf meta character and would cause interpolation problems?". I don't think the answer to that is short-sightedness.

The reason for % not interpolating has got to be something other than "because printf would be harder to use". chromatic's answer seems to provide a better explanation.

Update: What I meant to say is that if Larry wanted hashes to interpolate, he could've easily done so without having a major problem with printf (either by chosing another sigil for hashes or by changing printf's meta character).